Yes, they are top balanced, meaning they are all at the same state of charge.Will report back. They're just sitting there compressed without busbars.
They wait is really just to see how far apart they are in self discharge rate.
Top Balancing "How to"
- Thread starter snoobler
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They wait is really just to see how far apart they are in self discharge rate.
12 hours later and cell one is quite lower...these are listed as "Grade A cells". Thoughts after 12 hours?
| Cell | 7pm | 6:50am | Delta |
| 1 | 3.549 | 3.422 | 0.127 |
| 2 | 3.551 | 3.509 | 0.042 |
| 3 | 3.551 | 3.512 | 0.039 |
| 4 | 3.551 | 3.512 | 0.039 |
John Frum
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Dang.
One of these things is not like the other.
Do you have a capacity tester per chance?
Well, that cell has a higher self discharge rate than the others. It's not too bad. It certainly could be better.
The balance current in your BMS should be able to handle the difference.
I don't have a capacity tester or AC charger. All I have is the 4 batteries and my BMS. I can hook it up in series tonight, hook up the bluetooth and plug it into my van to run my 12v fridge and see if the batteries re-balance.
I'm camping next week and wanted these installed/ready to go before I leave.
Should I initiate the dispute process and if all works, just not return but if camping trip shows these batteries as a fail then ship back?
I'm camping next week and wanted these installed/ready to go before I leave.
Should I initiate the dispute process and if all works, just not return but if camping trip shows these batteries as a fail then ship back?
John Frum
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Discharging the cells alone won't fix anything.
@Just John thinks its not horrible and I am also inclined to wait and see.
What I was suggesting was to discharge a couple of amp hours out of each cell and then top them off individually.
Then put them in a serial pack with bms and cycle them down to ~50% as many times as possible before your trip.
The best way to charge them is with an ac charger as its deterministic and not dependent on the sun, but you have to work with what you have.
Do you have an alternator charger?
When you configure your bms make sure it only balances during the charge cycle and only above float voltage.
John Frum
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Since you don't have a capacity tester and I presume no other easy way to discharge the individual cells I suggest you make a pack and start cycling.
See how they cells behave.
Also you should do a capacity test if/when they are demonstrated to converge at the top.
You have an inverter, confirm?
See how they cells behave.
Also you should do a capacity test if/when they are demonstrated to converge at the top.
You have an inverter, confirm?
I have a renogy DCC30S that will prioritize the charge inputs. I'm going to follow Will's video on the OverkillBMS (mine is the same pcb, just different reseller) when he was setting it up. I'm guessing he puts in those settings, if not, I will search around here for details.
This forum has been so inviting and informative to newbies like myself without any pretentiousness or snobbery. Such a great group!
Hedges
I See Electromagnetic Fields!
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Could they have behaved that way because contact resistance kept some from charging as fast, and they just didn't absorb as fully?
I don't have experience using these, but would try topping off individually like Joey says.
When you do assemble your pack be sure to remove aluminum oxide, use corrosion inhibitor, and torque properly. At high current any contact resistance will cause problems.
I don't have experience using these, but would try topping off individually like Joey says.
When you do assemble your pack be sure to remove aluminum oxide, use corrosion inhibitor, and torque properly. At high current any contact resistance will cause problems.
We as a community don't have a huge depth of long term experience with these LiFePO4 cells. By long term I mean five years or more. We don't know what a laggard cell like you have is going to act like in two years. It could constantly be "different" than the other cells, but still last eight years. Or, it could die tomorrow.
We really don't know, but my guess is that it will work for years. Is the difference enough to bother you? Right now it is! But after a year of reliable service are you going to care as much about that difference?
We really don't know, but my guess is that it will work for years. Is the difference enough to bother you? Right now it is! But after a year of reliable service are you going to care as much about that difference?
I had to go back and check, you posted a picture of the cells hooked up to a power supply capable of 30v. That qualifies as an AC charger, just FYI.
Excellent suggestion by you and @smoothJoey . Individually topping the cells, and making sure connections are good is certainly recommended.
Oh...well then.
I'm new to this and since the amazon link mentions just "DC power supply", I didn't know that satiates both.Next steps I guess I'll take are to hook up the BMS (following Will's video to a T). I have a Traeger 400w alligator clamp style inverter that I could simply clip to the battery pack and run a laptop or electronic device. The BMS should have some discharge data as I don't have a shunt.
These smaller variances, the BMS should be able to handle, so I'll try to ease off anxiety and hook up my DC charger as my "alternator" with my Traeger inverter as a power draw.
John Frum
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Cool just make sure that if you use float that it is lower than the balance threshold set on the bms.I have a renogy DCC30S that will prioritize the charge inputs. I'm going to follow Will's video on the OverkillBMS (mine is the same pcb, just different reseller) when he was setting it up. I'm guessing he puts in those settings, if not, I will search around here for details.
This forum has been so inviting and informative to newbies like myself without any pretentiousness or snobbery. Such a great group!
And most important... don't balance on discharge.
Unless things really start circling the drain.
You might try leaving the fridge door open to increase battery drain. I wouldn't dispute yet, it is certainly possible a bad connection caused the saturation to not be as full as the others. If the BMS can keep them in balance, you shouldn't have too many problems in the future.
Really, it all just depends. Don't set the balance voltage below 3.4v, and charge to 3.45v and see if they come back relatively balanced. First just hook up your power supply to the single cell and try to get it saturated today, then tonight let the pack run the fridge (with the BMS) and see.
You don't even need to take them out of the pack if you already have them in one, you can just connect and charge that individual cell.
Silly question, but the single cell charging is the SAME as when I did parallel? Just set PS to 3.65, turn off, hook up cell, turn on PS and watch for amperage to be 0.01 ish?
No question is silly. Yes, same procedure, just use the positive and negative on the single cell. I wouldn't go below .1 amps to be honest, that's plenty. As a group of four, 1 amp is plenty low enough too. Those power supplies are not the best for stability, so verify voltage first before hooking up again, it could have drifted even if you didn't touch the knobs.
MisterSandals
Participation Medalist
Looking ahead slightly...
When you get around to assembling these cells into a battery, make sure that you put the lower capacity cells in positions 2 or 3 in your battery. Note that cell 1 is the negative end and cell 4 the positive end.
And, hopefully you've labeled your cells so your notes and numbers persist after you move or rearrange your cells. I recommend using letters as cell labels (A, B, C...) because the cell positions as noted in previous paragraph are numbers. Its easy to make notes that are nonsense when both cell labels and position are numbers...
The reasoning for putting your weaker cells into positions 2 and 3 are that BMS's draw power (+) from cell 4 and for some dang reason all the crazy stuff happens to cell 1 (you'll see).
When you get around to assembling these cells into a battery, make sure that you put the lower capacity cells in positions 2 or 3 in your battery. Note that cell 1 is the negative end and cell 4 the positive end.
And, hopefully you've labeled your cells so your notes and numbers persist after you move or rearrange your cells. I recommend using letters as cell labels (A, B, C...) because the cell positions as noted in previous paragraph are numbers. Its easy to make notes that are nonsense when both cell labels and position are numbers...
The reasoning for putting your weaker cells into positions 2 and 3 are that BMS's draw power (+) from cell 4 and for some dang reason all the crazy stuff happens to cell 1 (you'll see).
Thank you sir! Great callout. I still have the pack clamped together where Cell 1 (closest to PS when I was top balancing) is the one showing the biggest drop. I will put this cell on the negative side of the 2/3 and will be renamed B or C after I rename to letters from numbers already
. It looks like I might also have to cut my studs shorter to fit in my battery box as these stand proud about .5" and into a metal lid (that I will obviously put a closed foam protector on.
